Nowadays, electronic products, such as mobile phones, personal digital assistants (PDA) or laptop computers, are more lightweight and portable so that they are convenient for people to carry around. Sometimes, people would wear earphones to listen to the audio information provided by the electronic products.
However, there is not yet an earphone that contains an audio-adjusting mechanism that can adjust the sound feature. Therefore, some people would purchase multiple earphones respectively for different sound features, but it costs much money and is inconvenience.